Nowadays, the data access stack from Microsoft that is widely (sometimes only) talked about is the ADO.Net Entity Framework, [current version 4.1 ;June 2011 CTP available for download].
This has also led to some confusion within the developer community as to whether the old approach of plain ADO.Net is dead. The answer definitely is a "No" and the data access technology that you would use in your application boils down to multiple factors (not just one) such as the complexity of the Domain Model of your application , the learning curve of your development team for adapting the new technology , project time lines etc.
I would like share some pretty good reading materials on,
1) "Why use an OR/M" The Object-Relational Impedance Mismatch, by Scott Ambler
2) Which Data Access stack to use and when Data Access Technology Matrix
3) Some interesting chapter excerpts from the "Programming Entity Framework" book from Oreilly
Programming Entity Framework
Also, the Beta 2 version for Entity Framework from Oracle is available for download.
ODAC 220.127.116.11.40 Beta 2 for Entity Framework and LINQ to Entities